Method for determining an indication of an acuity level of a user

This application is the U.S. National Stage of PCT/EP2021/059702 filed on Apr. 14, 2021, which claims priority to PCT Patent Application PCT/EP2020/060934 filed on Apr. 17, 2020, the entire content of both are incorporated herein by reference in their entirety.

The invention relates to the field of computer implemented methods for determining an indication of an acuity level of a user and a corresponding computer program product and a device.

A large number of eye diseases exist, which may either be acquired due to visual behavior or physiological conditions or may at least in part be congenital, such that persons may be predisposed to develop a particular eye disease. In many of such instances, early diagnosis of a potential risk factor or developing eye disease may be essential so as to stall the development, improve the eye condition and/or cure the particular disease. For example, early diagnosis may result in an appropriate correction or medical therapy to reduce or remedy the experienced symptoms.

In order to assess the eye health, patients or people at risk of developing an eye disease are hence required to visit a medical professional such as an optometrist, wherein one or more tests may be performed to assist in assessing the eye condition and the patient's visual performance. Such visits to a physician's office or practice or medical institution may put a burden on the patient, in particular when the patient is required to perform such tests on a regular or periodical basis to track the development of the eye disease and/or the visual capacity of the patient.

Accordingly, it is preferred to perform such tests at a remote location, preferably at a patient's home. Whereas such tests are generally performed in a physician's practice on larger devices wherein both the patient and the device are at a particular position, such devices are absent at the patient's home. Therefore, the number of tests that may be performed at the remote location may be restricted to the available tools, which are—due to logistics and manufacturing costs—limited, thereby also putting constraints on the variability of such tests.

As an alternative, particular tests may be performed on computer or on devices capable of performing the required test, wherein a user may perform the test using a display of such device. However, as both the type of device and the ambient conditions may vary, it is generally difficult to ensure that the test is performed under equal and/or standard conditions. Currently, a user may only be provided with instructions to motivate the user to perform the test under the appropriate conditions and according to prescribed dimensions.

A number of eye diseases is related to the visual acuity, which is also referred to as the clarity of vision and is dependent on optical and neural factors, wherein low visual acuity may be due to refractive errors, such as aberrations in the shape of the eyeball or the cornea, astigmatism, and/or reduced flexibility of the lens. Such refractive errors may result in a nearsightedness or farsightedness of the user or patient. Furthermore, retinal diseases such as, for example, age related macular degeneration, may also be a cause of reduced acuity.

In order to assess the visual acuity, tests are generally performed while fixating and focusing the eye so as to provide a measure of central or foveal vision, as acuity is normally highest along the center. In addition, such tests may be based on the principle of Vernier acuity, which is a measurement of visual acuity that assesses the ability to discern the offset between two graduation segments sliding parallel to each other. When performing such tests, it is hence of importance to maintain a particular distance between the eye of the patient and the testing device, e.g. a display of a device, so as to ensure that the test is performed under the appropriate conditions and according to prescribed dimensions. That is considered critical, as the type of device may vary and the test conditions including the surroundings and the user's behavior may be inconsistent. By the same token, displays of various devices may have different characteristics and, in particular, may have varying resolutions, such that the tests may not be performed according to a common standard or under standardized conditions. Furthermore, an accuracy or assessing of the acuity level of such tests may furthermore be limited.

From WO 98/18381 A1 a visual acuity tester is known, which uses anti-aliasing to explicitly avoid any aberrations or distortions of standardized characters displayed on a customized display screen. In particular, the anti-aliasing is used for test characters by smoothing out the jagged edges that arise due to the inability of the ideal test character shape to be accommodated within the pixel array. Accordingly, the characters are displayed such that the user does not recognize any noticeable distortions and the characters are provided in a clear and centered manner so as to improve the appearance.

A further problem is lack of intuitiveness when actually performing the test, since such tests generally require that the user performs manual adjustments to correct for any displayed misalignments. Such manual adjustments may require the actuation of one or more buttons and may be time consuming and are hence not perceived as being user friendly. In addition, the risk of manual error is increased when performing the test under such conditions. Furthermore, manual adjustments may render it difficult to maintain conditions that are appropriate for performing the test, in particular since such tests are often time consuming.

Accordingly, there is a need for methods and devices to facilitate the performance of acuity tests in a decentralized manner while establishing a desired test accuracy, irrespective of a particular type of device so as to determine an acuity level of a user in a reliable manner.

It is an object of the present invention to provide a method and device for determining an acuity level of a user which improve the above undesirable problems.

Said object is achieved by the subject matter disclosed herein. Preferred embodiments are disclosed in the description, and the Figures.

Accordingly, in a first aspect, a computer implemented method for determining an acuity level of a user is suggested, which comprises the steps of

The use of the anti-aliasing enables that the range of possible discontinuities and hence the range of acuity levels to be measured may be increased. Accordingly, the discontinuity is generated and displayed based on anti-aliasing using one or more pixels of the display and using the control unit and the display.

Such anti-aliasing is based on the fact that pixels may not only be presented in black or white color, but may essentially comprise or exhibit any particular grayscale color therein between.

Although a user may more easily perceive a pixel shift of a black pixel, i.e. moving a black pixel towards an adjacent pixel and presenting the previous pixel position as a white pixel, he may not perceive a gradient shift, wherein e.g. a previously black pixel is reduced to 90 percent intensity and wherein an adjacent white pixel is increased to a black pixel intensity having a 10 percent pixel intensity. In other words, whereas in the first case a user may detect the pixel shift as a traversing pixel, he may not notice such gradient shift.

In particular for lines having a particular pixel thickness, e.g. 4 to 6 or 5 pixels, anti-aliasing may provide that an offset between such lines may not only be provided by full pixels, but by providing a gradient shift, wherein not only the outer pixels may contribute to such gradient shift, but also the pixels arranged more centrally may exhibit such gradient shift. Thereby, the accuracy and detail level of the acuity test may be further increased, such that support for medically significant acuity levels may be provided that were previously not identifyable using a standard display and using full pixel shifts.

Providing a discontinuity based on anti-aliasing may hence be considered as deliberately providing a deviation or (gradient) shift of a region of a structure of the graphical representation which may preferably be indicative of a particular acuity level, wherein the anti-aliasing enables an improved acuity testing resolution.

In addition, the resolution of the display is taken into account, such that the displayed acuity test may have varying dimensions depending e.g. on the size of the display and the pixel density. Therefore, the acuity test may be performed on a variety of devices without significantly modifying the appearance to a user.

For example, the computer implemented method may be performed on a laptop computer, notebook, tablet, or other portable hand-held device such as e.g. a mobile terminal or PDA, wherein the method may be implemented in a module or may be stored as computer-readable instructions stored on or otherwise provided to the device. Such instructions may then be executed by a control unit of the device, which, in certain embodiments, may be provided as a processor or integrated microprocessor, preferably communicatively coupled to an on-board memory and/or storage medium.

As outlined in the above, the display furthermore comprises or exhibits a resolution, which may be defined as a pixel density multiplied by the size or area of the display, wherein the area is defined by an extension of the display in a longitudinal direction of the device and a direction perpendicular to the longitudinal direction, e.g. a height and width of the display. Knowing the resolution of the display, the control unit may hence adjust or adapt the displayed acuity test so as to display the acuity test according to predefined dimensions.

The adaptation of the acuity test is not limited to a particular type of acuity test and may be implemented e.g. both when performing a test based on Vernier acuity and when testing variations in shapes. In either instance, the anti-aliasing provides that the accuracy and detail level of the acuity test may be further increased by providing gradient shifts rather than full pixel shifts.

The term “adjusting” is to be understood as including both an initial setting of the display and changing said settings during the performance of the acuity test, e.g. based on a user response. The adjusting or setting may be performed by providing a corresponding display or control signal to the display or display unit, thereby enabling the display to present the acuity test according to predefined dimensions.

When referring to predefined dimensions, it will be understood that the displayed acuity test may comprise a particular size and/or extension in at least one direction of the display. As described in the above, the control unit may output a control signal to the display—to e.g. increase the size or extension of the displayed acuity test, such that the acuity test may be displayed on only a portion of the display or extend over the display until essentially covering the entire display. The varying spanning furthermore depends on the resolution of the display, such that a display having a lower resolution may require a lower number of pixels to be activated compared with a display having a higher pixel density.

In order to further optimize the user's experience when performing the test, the displayed optical acuity test preferably comprises or essentially consists of a graphical representation displayed in black color on a white background. Such a feature, not only provides that the graphical representation is easily recognizable, but also reduces the perception of glare from ambient. In other words, even under conditions with strong ambient light, a user may still be able to see the graphical representation and is able to perform the acuity test without requiring considerable efforts that potentially render performing the acuity test difficult or strenuous.

The method enables performing various types of optical acuity tests, wherein the dimensions of the displayed acuity test may be accordingly adapted based on the resolution of the display. Preferably, the displayed optical acuity test comprises at least two lines, wherein the adjustment includes adjusting a size, length, and/or thickness of said lines. Accordingly, said lines may have the same overall appearance between a variety of devices having different resolutions.

For example, although the thickness of the lines may also consist of a predetermined number of pixels (e.g. 5 pixels), the width or thickness of the lines may be accordingly adapted such that e.g. (ultra) high resolution displays may use a larger number of pixels compared with displays having low resolutions, such that the thickness perceived by a user is essentially the same.

When performing the optical acuity test, the displayed optical acuity test comprises a graphical representation comprising a discontinuity and prompting the user to identify said discontinuity by providing a user response. Based on the user response, the optical acuity test may then be adjusted using the control unit.

The discontinuity may e.g. be provided as an irregularity of a shape, wherein the irregularity may be formed as an offset to a continuous line, e.g. by a circle having a bump or gap having a particular size or by two lines that arranged along a longitudinal axis, wherein said lines are offset in a perpendicular direction. Whereas larger discontinuities may more easily be identified by a user, smaller discontinuities may be less apparent and hence form a measure to determine the acuity level of the user. Based on the user responses, i.e. whether or not the user has correctly identified the discontinuity, the control unit may evaluate the user responses and determine the acuity level based e.g. on a scoring and/or averaging algorithm.

To further facilitate the interaction with the user performing the acuity test, the discontinuity is preferably aligned along a longitudinal direction of the display, wherein a user response is received by the control unit by a selection of an indication relating to the discontinuity, wherein the graphical representation comprises an indication on opposing ends of the graphical representation.

For example, rather than performing an adjustment or correction of a displayed misalignment, the user is merely required to indicate whether a discontinuity is present or not, such that the performance of the acuity test is facilitated and more intuitive, thereby improving the user experience and reducing the time required to perform the acuity test. Furthermore, this may also motivate a user to increase the frequency of performing such tests, such that the tests are more likely to be performed according to a prescribed interval. Thereby, it becomes more likely that the onset of e.g. macular degeneration or other factors that may influence or affect the acuity level of the user is detected at an earlier stage, such that a correction or medical treatment may be accordingly provided.

Having the indications at opposing ends furthermore ensures that the focus of the user is maintained in the center of the display, wherein the discontinuity is preferably displayed at the center. Thereby, any interfering objects and varying elements from the periphery of the device are screened out as much as possible and the display surrounding the graphical representation may be configured to provide a more homogenous appearance, when the user is performing the acuity test.

To further facilitate the user interaction and the performance of the acuity test, the display is preferably configured as a touchscreen, wherein the user response is received by the control unit by means of tactile interaction with the touchscreen at or in a direction of a region of the display corresponding to the indication. Such an approach ensures that the user may trigger the user response using interactions that may also be applied to other hand-held devices. The user may e.g. trigger the user response by means of tapping with a finger or swiping a finger from a central position on the display to the corresponding end comprising the indication. Thereby, no cumbersome adjustments are required and the user may maintain focused on the center of the display.

Furthermore, instead of e.g. detecting irregularities in shapes or selecting a shape having an irregularity compared with shapes having a continuous appearance, the graphical representation preferably comprises at least two lines. The at least two lines essentially arranged along a longitudinal direction of the display, wherein the discontinuity is formed as an offset of said lines in a direction perpendicular to the longitudinal direction of the display. As described in the above, the lines may hence be aligned essentially along the same axis so as to form a continuous line, yet are offset to each other starting from the connecting ends, i.e. in a staggered manner. In such case, the user may be required to indicate whether the lines form a continuous line or are discontinuous, wherein the displayed offset is a measure for the acuity level of the user.

Accordingly, it is preferred that the indication of the acuity level of the user is determined using the control unit and based on the user response.

To determine the indication of the acuity level, the acuity test may be performed by the control unit in two steps, wherein, in the first step, an indication of the initial acuity level is determined and, in the second step, said initial acuity level is refined and/or confirmed as an indication of a final acuity level. In other words, the first step may provide an estimate of the acuity level, whereas in the second step, a more exact test or fine-tuning of the indication of the acuity level is performed so as to resolve a final score or indicated acuity level. This has the advantage that the first step may be performed more rapidly while at the same time the two steps may be separated, i.e. be performed at different time points. This may be perceived as more comfortable, since the test is less time consuming and separation of the two steps may be less tiresome as the concentration timespan may be shortened.

The acuity test generally does not provide a diagnosis, although the result may be used as an acuity estimation and may obviate further tests. Instead, the acuity test generally provides an indication for a physician to assess the acuity performance to support performing a diagnosis.

In a preferred embodiment, in the first step, the graphical representation comprises a discontinuity corresponding to a first acuity level. If the user response correctly identifies the discontinuity, the control unit adjusts the acuity test by displaying on the display a further graphical representation comprising a discontinuity corresponding to a second acuity level and prompting the user to identify said discontinuity by providing a user response, the second acuity level being higher than the first acuity level. If the user response does not identify the discontinuity, the control unit sets the indication of the initial acuity level to a predefined initial acuity level being lower than the first acuity level.

The acuity level may be scored with reference to the Logarithm of the Minimum Angle of Resolution, also known as LogMAR values. Using such a scaling, it is considered that an observer who can resolve details as small as 1 minute of visual angle scores LogMAR 0, since the base-10 logarithm of 1 is 0. By the same token, an observer who can resolve details as small as 2 minutes of visual angle scores LogMAR 0.3, since the base-10 logarithm of 2 is near-approximately 0.3, wherein the higher value indicates a corresponding reduced visual acuity. Using the discontinuity, an offset in the graphical representation may hence correspond to a particular LogMAR value, such that starting from a first acuity level corresponding to e.g. a LogMAR value of 0.7, graphical representations comprising a continuity with increasing acuity levels may be displayed, ranging e.g. up to LogMAR−0.7. Should the user be unable to identify the first acuity level, the indication of the initial acuity level or estimate threshold may be set to a lower acuity level, e.g. LogMAR 1.0.

On the other hand, if the user response correctly identifies the discontinuity according to the second acuity level, the method further may comprise performing the step of adjusting the acuity test by displaying, using the control unit, on the display a further graphical representation. It may comprise a discontinuity corresponding to an acuity level being higher than the previous acuity level with a predefined amount and prompting the user to identify said discontinuity by providing a user response. Said step is typically repeated until a predefined maximum acuity level is achieved, if the user response correctly identifies the discontinuity, thereby achieving an indication of the initial acuity level, or until the user response does not identify the discontinuity.

Following the above example, a user may be presented with a discontinuity corresponding to a first acuity value of LogMAR 0.7. After having identified the discontinuity, the subsequent graphical representations that are displayed comprise a reduced LogMAR value, i.e. having a higher acuity value, with a predefined amount, such that the second graphical representation may correspond to a LogMAR value of e.g. 0.4 and wherein the predefined amount or Δ value is 0.3. By the same token, should the discontinuity according to the second graphical representation be correctly identified, a third graphical representation is displayed, wherein the discontinuity is adjusted so as to obtain a LogMAR value of 0.1, and so on, until a predefined maximum LogMAR is achieved of, for example, −0.7. The predefined amount may vary between each step, such that e.g. a first set of graphical representations may correspond to larger visual acuity differences and differences between discontinuities towards the maximum LogMAR value are smaller, so as to provide an improved estimate of the initial acuity level.

However, if the user response does not identify the discontinuity, e.g. the second or subsequent discontinuity, the method may further comprise performing the step of adjusting the acuity test by displaying, using the control unit, on the display a further graphical representation. The further graphical representation may comprise a discontinuity corresponding to an acuity level being lower than the previous acuity level with a predefined amount and prompting the user to identify said discontinuity by providing a further user response, wherein

Again, following the above example based on LogMAR values, the second acuity level may e.g. correspond to a LogMAR value of 0.4. Should said discontinuity not be identified, the control unit may increase the LogMAR value by a predefined Δ value of, for example, 0.2, such that the subsequent discontinuity that is displayed corresponds to a LogMAR value of 0.6. By the same token, should the user identify e.g. the second and third discontinuity, the third discontinuity corresponding to a Δ value of e.g. −0.1, and does not identify the fourth discontinuity having a LogMAR value of e.g. 0.4, the control unit increases the LogMAR value by a predefined Δ value of e.g. +0.1, such that the display displays a further graphical representation having a LogMAR value of 0.5.

In such a scenario, there are two options. If the user does not identify the discontinuity, further graphical representations are subsequently displayed prompting the user to identify the discontinuity, wherein the LogMAR value of each subsequent discontinuity is increased by a predefined amount or Δ value. This sequence is stopped, once a discontinuity is correctly identified or until the first acuity level is achieved. For example, if the graphical representation having a LogMAR value of 0 is not identified, the next discontinuity may correspond to a LogMAR value of 0.1. If the user identifies said discontinuity, the indication of the initial acuity level is set to a LogMAR value of 0.1. However, if the user does not identify any of the subsequent discontinuities and the first acuity level of e.g. 0.7 is reached, the control unit will set the indication of the initial acuity level to the first acuity level.

Alternatively, to reduce potential error and to speed up the acuity test, i.e. the first step of the acuity test, the indication of the initial acuity level may also be set to the acuity level corresponding to the previously displayed discontinuity, once a total of two discontinuities, preferably subsequent, have not been identified.

The second option provides that the acuity test is adjusted, if the further user response identifies the discontinuity, by displaying a further graphical representation comprising a discontinuity corresponding to an acuity level being higher than the previous acuity level with a predefined amount and prompting the user to identify said discontinuity by providing a further user response. For example, the initial increase in the LogMAR value up to e.g. 0 may be identified by the user, wherein the subsequently displayed graphical representation comprises a discontinuity corresponding to a LogMAR value of −0.1, e.g. wherein lowering of the LogMAR value is performed with a predefined amount or Δ value of 0.1. This step both provides an initial finetuning and a reduction of any potential statistical error. If the user identifies the subsequent discontinuity, said step is repeated until a discontinuity is not identified, e.g. corresponding to a LogMAR value of −0.3, wherein the indication of the initial acuity level is set to the acuity level corresponding to said value. By the same token, should the user reach the maximum acuity level, e.g. corresponding to a LogMAR value of −0.7, the indication of the initial acuity level is set to the acuity level corresponding to the maximum LogMAR value.

After having obtained the indication of the initial acuity level, the method may perform the second step, wherein a pool of graphical representations is generated, each graphical representation comprising a discontinuity corresponding to a specific acuity level. The pool typically comprises a predefined number of graphical representations having a discontinuity according to the indication of the initial acuity level and further comprises a predefined number of graphical representations having a discontinuity corresponding to an acuity level being higher than the indication of the initial acuity level with a predefined amount, i.e. corresponding to a lower LogMAR value. The acuity test is adjusted by displaying, using the control unit, on the display a randomly selected graphical representation from said pool and by prompting the user to identify said discontinuity, wherein the method comprises the step of

The indication of the initial acuity level may be obtained corresponding to e.g. a LogMAR value of −0.3. In this case, the pool is generated by including a predefined number, e.g. three, graphical representations having a discontinuity corresponding to −0.3. Furthermore, the pool includes a predefined number of graphical representations having a discontinuity with a higher acuity level, wherein the predefined amount may correspond to e.g. a LogMAR delta value of 0.1, such that a predefined number, e.g. also three, of graphical representations having a discontinuity corresponding to −0.4 is added to the pool. The predefined numbers, although this may be provided in an embodiment, are merely provided for exemplary purposes and may be different for each group of graphical representations or acuity level. By the same token, the predefined amount may also correspond to higher or lower values, depending on the desired accuracy of the acuity level to be determined.

After said pool is generated, a random graphical representation is displayed and the user is prompted to identify said graphical representation. In this case, the user may either correctly identify the discontinuity or may perceive the discontinuity e.g. as a continuous graphical representation. In the former case, a predefined number of graphical representations having a discontinuity corresponding to an acuity level being higher than the indication of the initial acuity level with a predefined amount is added to the pool. However, this is only the case, if a graphical representation having a discontinuity corresponding to said acuity level has not yet been added to the pool and the level does not exceed a predefined amount from the indication of the initial acuity level.